Repeat Prob. 11-56 for a heat exchanger pressure of 0.55 MPa.
Prob. 11-56
Consider a two-stage cascade refrigeration system operating between the pressure limits of 0.8 and 0.14 MPa. Each stage operates on the ideal vapor-compression refrigeration cycle with refrigerant-134a as the working fluid. Heat rejection from the lower cycle to the upper cycle takes place in an adiabatic counter-flow heat exchanger where both streams enter at about 0.4 MPa. If the mass flow rate of the refrigerant through the upper cycle is 0.24 kg/s, determine
(a) The mass flow rate of the refrigerant through the lower cycle.
(b) The rate of heat removal from the refrigerated space and the power input to the compressor.
(c) The coefficient of performance of this cascade refrigerator.